This application claims the priority of application No. 100 37 062.4, filed Jul. 29, 2000, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a fuel cell comprising (1) a gas generation device for catalytic steam reforming of a steam/fuel mixture and/or for the partial oxidation of an oxygen/fuel mixture for generating a product gas containing hydrogen-rich medium; and (2) a gas cleaning stage for removing carbon monoxide from the product gas by selective CO oxidation.
In the cold-start phase, a polymer electrolyte membrane (PEM) fuel cell system is operated in operating states which are not optimum, which represents a drawback in particular for the reactions in the gas generation system that are thermally adapted to one another. However, when starting up, the gas generation system has to be brought to operating temperature. In the case of a cold start, this leads to water or water/methanol mixture condensing out upstream of and in the gas cleaning stage. This condensation leads to wetting of the active catalyst surface in the reactor and therefore to the starting time being extended.
DE 197 27 588 A1 discloses a device and a method for generating a hydrogen-rich gas that is low in carbon monoxide. The product gas containing hydrogen and carbon monoxide is generated in a gas generation device from a water/fuel mixture by catalytic steam reforming and/or from an oxygen/fuel mixture by partial oxidation. In a gas cleaning stage, the carbon monoxide content in the product gas is lowered by selective CO oxidation at an oxidation catalyst. In this document, it is also proposed that, in order to improve the cold-start properties, for oxygen to be admixed with the fuel supplied during a starting phase and for the direction of flow to be reversed in such a manner that the media flow first through the gas cleaning stage and only then through the gas generation device.
An object of the present invention is to provide a fuel cell system having acceptable cold-start properties.
This object is achieved by a device according to the present invention.
According to the present invention, flow-diverting means are provided in a fuel cell system, in order to open or block flow paths for a medium in a temperature-dependent manner.
Compared to the prior art, the fuel cell system according to the present invention results in a simple solution without complex additional components.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.